Field of the Invention
The present invention relates to the field of lithium secondary batteries of high energy density, particularly relates to a novel preparation method of carbon-selenium nanocomposite materials and their applications.
Description of Related Art
With the increasing human demand for energy, secondary batteries with high energy density and high volume energy density, such as lithium-sulfur batteries and lithium-selenium batteries, have attracted widespread interests. Group 6A elements in the periodical table, such as sulfur and selenium, have shown two-electron reaction mechanisms in the electrochemical reaction process with lithium. Despite the theoretical mass energy specific capacity of selenium (675 mAh/g) is lower than that of sulfur (1675 mAh/g), selenium has a higher density (4.82 g/cm3) than sulfur (2.07 g/cm3); therefore the theoretical volume energy density of selenium (3253 mAh/cm3) is close to the theoretical volumetric energy density of sulfur (3467 mAh/cm3). At the same time, as compared with sulfur, close to an electrically insulated material, selenium is semi-conductive electrically and shows better electrically conductive property. Therefore, as compared to sulfur, selenium can demonstrate a higher level of activity and better utilization efficiency even at a higher loading level, leading to high surface density battery systems. Moreover, selenium-carbon composite can have a further improvement in the electrical conductivity over sulfur-carbon composite to obtain a higher activity electrode material. As described in the patent CN104393304A, by passing hydrogen selenide gas through graphene dispersion solution, the solvent heat reduces the graphene oxide into graphene while oxidized the hydrogen selenide into selenium. The such prepared selenium graphene electrode materials pairs with ethers electrolyte system, 1.5M lithium bi-trifluoromethane sulfonimide (LiTFSI)/1,3-dioxolane (DOL)+dimethyl ether (DME) (Volume ratio 1:1); the charging specific capacity reaches 640 mAh/g (approaching selenium theoretical specific capacity) in the first cycle. But in the charge-discharge process, polyselenide ions dissolve in the electrolyte, showing significant amounts of the shuttling effect, which causes the subsequent capacity delay. At the same time, the procedures for preparing the graphene oxide raw material that is used in this process are complicated, not suitable for industrial production. CN104201389A patent discloses a lithium-selenium battery cathode material, utilizing a nitrogen-containing layered porous carbon component current-collector which was compounded with selenium. In preparing nitrogen-containing layered porous carbon composite current collector, nitrogen-containing conductive polymer is first deposited or grown on the surface of a piece of paper, followed by alkali activation and high temperature carbonization, resulting in a nitrogen-containing layered porous carbon composite current collector with carbon fiber as network structure that supports itself; and such nitrogen-containing layered porous carbon composite current collector is then further compounded with selenium. The deposition method for preparing a conductive polymer is complicated and the process for film formation or growth is hard to control. The preparation process is complicated, which associates with undesirably high costs.